1. Field of the Invention
The present invention relates to an apparatus and method for remote tracking and monitoring of persons and more particularly to attitude determination of a remotely monitored device which is periodically or permanently attached to the body of a monitored person.
2. Discussion of the Related Art
Currently, remote tracking and monitoring of persons are achieved via the utilization of radio and cellular technologies. Typically, a body-worn electronic tag and an optional tracking, processing and reporting device that communicates with the electronic tag, are attached to the monitored person's body, where the tag or the associated tracking device is periodically or continuously broadcasts a radio signal to a local or remote monitoring station via a cellular site. The signal includes tracking information in encoded format where the information could contain one or more types of tracking data, such as location data, and/or device attitude data where the device is periodically or permanently attached to the body of the monitored person. Location data indicates the geographical location of the monitored device while attitude data indicates the position of the monitored device relative to a frame of reference, such as the vertical-horizontal axis. In accordance with the specific application, the apparatus could be adapted to handle different types of relevant tracking information. Thus, for example, a legally movement-restricted or location-restricted person, such as a convicted criminal offender under house arrest, could be monitored by the collection of both location data and attitude data in order to make sure that location-restriction or movement-restriction order is properly maintained
Location data could be determined either in accordance with the identification of the signaling path, through cellular or Global Positioning System satellites (GPS)-assisted triangulation techniques, or other location-finding techniques while device attitude data could be collected by specialized electromechanical devices such as inertial measurement devices, or tip-over switches.
Device attitude represents the position or the arrangement of either a non-attached or a body-attached device when situated in space relative to the vertical-horizontal axis frame. In remote personal tracking and monitoring systems a device attitude detector and indicator is an electromechanical apparatus that detects the attitude of a non-attached or body-attached device relative to a frame of reference, such as the vertical-horizontal axis, and informs the monitoring station of the detected attitude. The device attitude detector apparatus is typically used for detecting and indicating whether the non-attached monitored device or the body-attached device and therefore the body of the monitored person to which the device is attached is in a standing position (vertical) or in a lying down position (horizontal). The known instruments used for attitude detection are multi-axis motion sensors, such as traditional gyroscopes (gyros), inertial measurement units (IMUs) or solid-state miniature tri-axial gyroscopes. In some remote personal tracking and monitoring systems 3 degrees of freedom motion sensors are used to assist in determining if the unit is in motion. Determining whether the unit is in motion is important from a number of reasons. One of the reasons is to determine the location of the tracked individual through receiving GPS data associated with the individual location. Another reason is to conserve battery power by changing the GPS mode to a battery conserving mode if the individual is not in motion. There are number disadvantages in the above now used devices. One disadvantage lies in the sensitivity of such sensors, whereby each movement would trigger the device to determine that the individual being tracked is moving, while in fact, such individual has not moved at all. Another disadvantage lies in the fact that now used sensors, which do not comprise inertial detectors, are not likely to detect very slow movement. Thus, an offender may move around very slowly without activating the GPS and thus will be able to change his position without detection. As a result using these devices in human personal monitoring where the requirements for attitude information are considerably simpler is not cost effective and is too cumbersome. There is therefore a need in the art to provide a simple and cost effective mechanism which will be effective in determining when an individual being monitored using a GPS tracking and monitoring unit has moved from one location to another, while activating the unit's GPS only when necessary.